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Joining

11.1.1 Describe friction welding.

Friction welding is a completely mechanical solid-phase process in which heat generated by friction is used to create the ideal conditions for a high-integrity welded joint between similar or dissimilar metals.

11.1.2 Explain how two metal parts are welded using friction.

Diagrams should include two parts, one revolving, and the other fixed.

11.1.3 Describe plastic welding.

Consider hot air and friction welding techniques.
  • Wikipaedia reference.
  • Below video on hot air welding

11.1.4 Explain how two plastic parts are welded together.

Only thermoplastics that do not burn or decompose when heated to their softening temperature can be welded.

11.1.5 Define permanent joining techniques.

Permanent joining techniques
A permanent join is a type of fastening that is not supposed to be removed. It is only possible to remove such joins by drilling, cutting or grinding the join away.

11.1.6 List a range of permanent joining techniques.

Consider pop-rivets, brazing, welding and adhesives.
Pop-rivets Welding

Brazing Adhesives (Glues)

11.1.7 Discuss how permanent joining techniques lead to planned obsolescence and environmental issues.

Permanent joins do not allow for the disassembly and easy maintenance of products.

11.1.8 Define adhesive.

Adhesive
An adhesive is a substance that is applied between two surfaces in order to bond them together.

11.1.9 Identify a range of adhesives suitable for joining metals, woods and plastics.

PVA (polyvinyl acetate), epoxy resin, contact adhesive, cascamite, tensol cement and superglue (cyanoacrylate).
Material Adhesive
Wood PVA (polyvinyl acetate), epoxy resin, contact adhesive (applying laminates),cascamite,
Metal Epoxy resin, superglue (cyanoacrylate)
Plastic Epoxy resin (some plastics), contact adhesive (neoprene), tensol cement, superglue (cyanoacrylate)
PVA - Elmers Epoxy Resin Contact Adhesive
Cascamite Tensol Cement Superglue (cyanoacrylate)

11.1.10 Discuss the advantages and disadvantages of using adhesive bonding in products.

Consider preparation of surfaces, clamping, bonding time, type of material, and health and safety.
Advantage Disadvantage
Preparation of surfaces * No drilling of holes, etc * Surface must be carefully cleaned
Clamping * Join all shapes and thicknesses
* Provide smooth contours
* Jigs and fixtures may be needed
* Heat and pressure may be required
Bonding time * Long curing time allows for repositioning (Disadvantage as well) * Long cure times may be needed
Type of material * Join all shapes and thicknesses
* Dissimilar materials can be bonded
* Certain adhesives are needed for the type of material.
Health and safety * Fumes can be toxic
* Human tissue can be bonded

Adhesives present several distinct advantages over conventional methods of bonding:

  1. Provide large stress-bearing area
  2. Provide excellent fatigue strength
  3. Dampen vibration and absorb shock
  4. Minimize or prevent galvanic corrosion between dissimilar metals
  5. Join all shapes and thicknesses
  6. Provide smooth contours
  7. Seal joints
  8. Join any combination of similar or dissimilar materials
  9. Often less expensive and faster than mechanical fastening (can be automated)
  10. Heat, if required, is too low to affect metals parts
  11. Provide attractive strength-to-weight ratio.

However, there are also disadvantages which may make adhesive bonding impractical:

  1. Surface must be carefully cleaned
  2. Long cure times may be needed
  3. Limitation on upper continuous operating temperature
  4. Heat and pressure may be required
  5. Jigs and fixtures may be needed
  6. Rigid process control usually necessary
  7. Inspection of finished joint difficult - Non distinctive testing not always possible
  8. Useful life depends on environment
  9. Special training is often required.

Quoted from http://www.bostik.com/products-services/products-services.php?id=1023&idtype=257


References

Bulleted list and italicised paragraphs are excerpted from Design Technology: guide. Cardiff Wales, UK: International Baccalaureate Organization, 2007.

Images are clickable links to its location.

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Page last modified on April 10, 2014, at 06:56 PM